A Local Area Augmentation System (LAAS) is Global Positioning System (GPS) Landing System (GLS) used at some airports as a primary or auxiliary landing system for certain runways. The system comprises a ground-based radio receiver that receives signals from a plurality of satellites of the Global Positioning System, and a transmitter that is used to communicate a digital signal comprising certain navigation and landing information to aircraft wishing to avail themselves of the GLS as an aid to landing on the runway to which the GLS is dedicated.
It is possible that one or more of the satellites of the Global Positioning System may fail. In addition, the Global Positioning System is operated under the control of the U.S. Government, which can modify the accuracy of the GPS in the event of, for example, the use of the GPS by enemy aircraft or missiles. Thus the ground-based GPS receiver continually monitors the satellites for failure or inaccuracy and relates a correction factor as well as navigation and landing information to the aircraft.
In addition to the navigation and landing information carried on the digital uplink from the ground-based transmitter, LAAS systems transmit to the aircraft identification signals providing frequency and runway information that the pilot (or crewmember) of the aircraft can use to confirm that the transmission being received is for the runway and airport at which it is desired to land. Presently, unfortunately, all runway identifiers and radio frequencies are not unique.
In modern aircraft specifically equipped to implement a LAAS landing system, the aircraft radios, in conjunction with the aircraft's flight management system, are capable of automatically providing to the pilot confirmatory information regarding the frequency and runway of the LAAS station being received. In such systems, the destination runway may be entered into the flight management system as a part of the flight plan. The flight management system looks up the proper frequency for the LAAS system for the destination runway, tunes the appropriate radio to the frequency of the LAAS and automatically confirms, by monitoring the uplink signal from the LAAS that the information being received is from the proper LAAS station.
Retrofitting older aircraft without making extensive changes to the flight management system and cockpit display system, however, can leave the pilot with workload intensive methods to properly confirm station and runway identification signals. It would be advantageous to provide a retrofit controller capable of translating the radio signals transmitted by the LAAS ground-based unit into visual or aural signals to assist the pilot in properly identifying the radio station to which his radio is tuned.